Wireless communications and wireless communication devices are at the center of many important technological advancements. As the proliferation of these wireless devices increases, the efficiency and accuracy of the communications therebetween becomes vital to the commercial success of particular devices and particular communications protocols. One protocol that is showing great promise is Bluetooth (described in, for example, The Specification of the Bluetooth System, v1.0 B, Dec. 1, 1999), which is a wireless protocol that describes how mobile phones, computers, PDAs, peripherals and other devices can interconnect using a short-range wireless connection. The Specification of the Bluetooth System, v1.0 B, Dec. 1, 1999, which is publicly available, is incorporated herein by reference.
To implement Bluetooth and other such wireless protocols, a device receiving a transmitted signal is required to recover transmitted bit patterns. The basic recovering process involves waveform demodulation, DC compensation, bit synchronization and bit detection. Waveform demodulation usually is implemented in a radio module and is wireless protocol dependent. DC compensation can be implemented either in the radio module or in the baseband. It is a critical process, however, for achieving correct bit synchronization and detection. Bit synchronization and detection are usually implemented in the baseband and are common to many different wireless receivers. An automatic DC tracker and a bit synchronizer have been described in commonly owned and assigned patent application Ser. No. 10/035,567, filed Oct. 22, 2001.
DC offset is a variation in the intended DC voltage of the baseline signal caused, for example, by frequency drift in received Bluetooth GFSK signals. Present devices compensate for these imperfections in incoming signals using a variety of means—none of which are completely satisfactory. For example, certain electronic devices use analog components to calculate the DC offset, while other devices use digital components. The analog DC trackers usually are implemented as lowpass RC filters, while conventional digital approaches require a select number of bits to be buffered before any DC offset can be calculated.
The DC tracking accuracy of both conventional analog and digital circuits is affected by the incoming bit patterns. For instance, when a string of high values, e.g., “1s,” is received the computed DC offset will be adjusted to a higher value even though the actual DC offset has not changed. This adjustment occurs because most automatic DC trackers assume an even distribution of high and low values in the received signal. In addition, the DC tracking accuracy and associated estimate variance are sensitive to selected time constant in analog filters. For conventional digital DC tracker, they are functions of the selected buffer size.
Although present analog and digital approaches to computing DC offsets for wireless communications are functional, they are not sufficiently accurate or otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.